drm/suballoc: Extract amdgpu_sa.c as generic suballocation helper

Suballocating a buffer object is something that is not driver-specific
and useful for many drivers.

Use a slightly modified version of amdgpu_sa.c

v2:
- Style cleanups.
- Added / Modified documentation.
- Use u64 for the sizes and offset. The code dates back to 2012 and
  using unsigned int will probably soon come back to bite us.
  We can consider size_t as well for better 32-bit efficiency.
- Add and document gfp, intr and align arguments to drm_suballoc_new().
- Use drm_printer for debug output.

v3:
- Remove stale author info (Christian König)

v4:
- Avoid 64-bit integer divisions (kernel test robot <lkp@intel.com>)
- Use size_t rather than u64 for the managed range. (Thomas)

Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Co-developed-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Signed-off-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Acked-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Acked-by: Alex Deucher <alexdeucher@gmail.com>
Acked-by: Christian König <christian.koenig@amd.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230224095152.30134-2-thomas.hellstrom@linux.intel.com

drivers/gpu/drm/Kconfig

@@ -231,6 +231,10 @@ config DRM_GEM_SHMEM_HELPER
 	help
 	  Choose this if you need the GEM shmem helper functions
 
+config DRM_SUBALLOC_HELPER
+	tristate
+	depends on DRM
+
 config DRM_SCHED
 	tristate
 	depends on DRM

drivers/gpu/drm/Makefile

@@ -88,6 +88,9 @@ obj-$(CONFIG_DRM_GEM_DMA_HELPER) += drm_dma_helper.o
 drm_shmem_helper-y := drm_gem_shmem_helper.o
 obj-$(CONFIG_DRM_GEM_SHMEM_HELPER) += drm_shmem_helper.o
 
+drm_suballoc_helper-y := drm_suballoc.o
+obj-$(CONFIG_DRM_SUBALLOC_HELPER) += drm_suballoc_helper.o
+
 drm_vram_helper-y := drm_gem_vram_helper.o
 obj-$(CONFIG_DRM_VRAM_HELPER) += drm_vram_helper.o